The present invention generally relates to level display devices for audio signals, and more particularly to a level display device for audio signal constructed to display bars having lengths corresponding to the input signal levels on a picture tube.
Generally, when recording an audio signal, there are cases where it is desirable to carry out recording by increasing or decreasing levels in a predetermined frequency band. In addition, when degradation is introduced in the fidelity of a reproduced audio signal in a reproducing apparatus due to effects caused by the frequency characteristics of audio equipment themselves such as speakers and pickup cartridges, the transmission characteristic of a listening room, and the like, there are cases where it is desirable to correct the levels in a predetermined frequency band. Further, there are cases where the frequency characteristic is not made flat during the recording and reproduction, and the frequency characteristic is set to a predetermined characteristic according to the needs. In the above described cases, graphic equalizers capable of variably adjusting the signal level in each of the divided frequency bands are used. When adjusting the level by the graphic equalizer, a level display device is used for displaying the levels throughout the entire band of the input signal and the signal levels in each of the frequency bands.
A conventional level display device was constructed to illuminate a number of light emitting diodes corresponding to the number of input signal levels. Moreover, another conventional level display device was constructed to display bars having lengths corresponding to the input signal levels on a screen of a picture tube.
However, in the above conventional level display devices, numerals for indicating each of the frequency bands, and numerals or scales indicating the level of the signal, are marked on a manipulation panel and the like. Accordingly, there was difference in brightness between the above numerals or scale and the level indication part such as bars displayed on the screen of the picture tube, and there was a disadvantage in that it was difficult to accurately read out the indication visually.
On the other hand, another conventional level display device was constructed to display with no difference in brightness between channels, when displaying the bars of right and left channels side by side, for example. Thus, in this conventional device, it was difficult to discriminate the channels, and there was a disadvantage in that the read out may be erroneously performed.
Further, another conventional level display device was provided with a logarithmic amplifier for each of the frequency bands, for logarithmicly converting the level of the input signal. Hence, this conventional device was easily affected by the ambient temperature, and for this reason was unable to display the correct levels. In addition, there was a disadvantage in that the circuit was complex.
In another conventional level display device, the bars were not displayed while the input signal is not supplied thereto. Accordingly, in this conventional device, the starting positions of the bars were unclear when there is no input signal. Therefore, there was a disadvantage in that it was difficult to visually read out the character display of the frequencies in correspondence with the bars.
Furthermore, in another conventional level display device, scale lines were not displayed on the screen. Accordingly, in this conventional device, there was a disadvantage in that it was difficult to read out the levels of the bars.